1. Field of the Invention
The subject invention generally pertains to the metering roll of a printing press, and more specifically to cleaning the metering roll.
2. Description of Related Art
In a printing process, a metering roll (anilox roll) transfers ink to a plate, which in turn applies the ink to the material being printed, such as paper or a consumer product label. Some metering rolls have a ceramic coating covered with a dense matrix of extremely small cells that hold the ink. Over time, the cells get plugged with dried or otherwise cured ink which reduces the effectiveness of the roll.
Currently, metering rolls are cleaned of their contaminants (e.g., dyes, ink, binders, plasticizers, etc.) with strong solvents, soda blasting, and ultrasonic processes. These methods, however, have limited effectiveness and serious drawbacks.
Many water-based dyes and inks are resistant to common solvents. Some solvents can no longer be used, because of their negative effect on the environment. Since ceramic can be porous, some solvents and/or chemicals penetrate completely through the ceramic coating to attack the roll""s metal core. This can lead to the ceramic coating separating from the roll. Excessive heating can also damage the interface between the roll""s metal core and the ceramic, due to the differences of their thermal expansion properties. Ultrasonic and soda blast cleaning can physically damage the ceramic itself. And today""s conventional methods of cleaning require that the metering roll be removed from the printing press. Moreover, there is a trend toward providing metering rolls with ever smaller hole diameters, which make the cells even more difficult to clean.
To avoid the limitations and problems of existing methods of cleaning metering rolls, it is an utmost primary object of the invention to shape the intensity distribution of a laser beam to match the curved geometry of the cells of a ceramic coated metering roll.
A second object of the invention is to employ an anilox cell geometry that promotes a smooth pattern of airflow delivered by an air nozzle that provides an angled approach.
A third object is to focus a laser beam toward a focal point that is below the bottom of the cell being cleaned.
A fourth object is to use heat to destroy the contaminants of a metering roll while minimizing the heat conducted to the roll""s metal core.
A fifth object is to provide a non-contact method of removing contaminants from a plugged metering roll, regardless of the hole diameter of the cells.
A sixth object is to clean a metering roll without having to remove it from the printing press.
A seventh object is to turn the laser beam off as it passes between cells to minimize the heat delivered to the roll.
An eighth object is to employ a guide bearing that maintains a constant separation distance between the lens and the ceramic surface of the metering roll, regardless of slight misalignments of the cleaning apparatus and cylindrical discrepancies of the roll.
A ninth object is to have the laser beam target travel in a helical pattern around a metering roll, with the pattern being superimposed on a similar helical pattern of cells.
A tenth object of the invention is to adjust the focus of the laser beam by test burning the ink off a paper label.
An eleventh object of the invention is to rotate a metering roll using a xe2x80x9cnon-slipxe2x80x9d synchronous motor whose speed is substantially constant, regardless of slight variation in torsional load.
A twelfth object is to compensate for limited encoder resolution by periodically delaying the firing time of the laser in response to an encoder compensation input.
These and other objects of the invention are provided by a novel apparatus and method for cleaning a ceramic coated metering roll. The method uses a laser that is uniquely focused to provide a beam intensity profile that suits the multiple curved surfaces of cells that are plugged with a polymeric contaminant. The laser applies heat to the roll at a temperature that destroys the contaminant yet leaves the ceramic coating intact. The heat is rapidly delivered and rapidly removed from the roll to minimize the amount of heat conducted to the roll""s metal core.